There are at least two kinds of paradoxes. Propositions that logically contradict themselves (such as the proposition that “Pencils are not pencils”) may be called logical paradoxes. Propositions that logically contradict being known by us (such as the proposition that “It is raining, but we don’t believe it”) may be called pragmatic paradoxes[2]. Note that logical paradoxes are paradoxical to everyone, but (some) pragmatic paradoxes are only paradoxical to certain people. For example, the proposition “It’s raining, but I don’t believe it” is paradoxical to me, but not to you. It would be paradoxical for me to know it, for to do so would require that I both believe and disbelieve that “It’s raining”. However, nothing about this proposition would make it especially paradoxical for you to know it, if it were true.
Does the relativism of pragmatic paradoxes mean that we should treat them any differently from logical ones? Not much. We should, of course, label the paradoxes differently, but any reasons for disbelieving logical paradoxes are also be reasons for us to disbelieve any propositions that happen to be pragmatically paradoxical for us. The avoidance of logical paradoxes is built-in to most systems of logic. Kant deserved some credit for realizing that avoidance of pragmatic paradoxes should figure into such systems as well. In sections three and four, I will suggest how this might be done.
Propositions that are paradoxical all by themselves are oddities that most people encounter only rarely. More often, we deal with paradoxes that arise from combinations of beliefs. For example, suppose Jason thought that his daughter, Mandy, was in school, but then saw her playing in a neighbor’s yard (which is not in school). Neither the proposition “Mandy is in school”, nor the proposition “Mandy is in the neighbor’s yard (which is not in school)” is paradoxical by itself, but they are logically paradoxical in combination. Thus, when Jason sees Mandy in the neighbor’s yard, he may feel obliged to reevaluate his beliefs—Are his eyes deceiving him? Or was he wrong to think that Mandy was in school? In such situations, recognition of paradoxes can be extremely useful. It is only because Jason has a policy of disbelieving paradoxes that he can utilize his observation to recognize Mandy’s truancy. Similarly, even if he held no previous belief regarding the whereabouts of his dog, Sam, Jason’s policy of avoiding paradoxes would allow him use an observation of Sam in a neighbor’s yard to decide that Sam also is not in school (nor in the house). Here Jason takes advantage of the potential for paradox in the combination of his beliefs.
The paradoxes that arise in combinations of beliefs are not only most often useful—they are also the most likely to go unnoticed. Propositions can combine in complex ways to yield implications. It has taken mathematicians hundreds of years to figure out how certain propositions are implied by certain small sets of axioms. Compared to such sets of axioms, our personal sets of beliefs are tremendously numerous. Imagine, then, how much more difficult it would be to identify all of the paradoxes and potential paradoxes in a typical person’s full set of beliefs! The grand prospects for unrecognized paradoxes and potential paradoxes make it plausible that a great deal of belief modification could result from mere reflection on our current beliefs, independent of gathering new observations. Let’s call this activity of seeking paradoxes and potential paradoxes in our beliefs “paradox testing”.
What is the status of “paradox testing” relative to empirical testing? In his Republic, Plato used his famous allegory of the Sun, Line and Cave to describe the path to knowledge as consisting of four consecutive stages. The first stage is that of holding beliefs. The second is that of knowing what those beliefs are. The third is that of knowing that they do not contradict each other (i.e. the result of paradox testing). The fourth is complete knowledge of the truth. By this account, paradox testing comes before the test of truth. In other words, non-paradoxical false beliefs may pass to the third stage, but paradoxical true beliefs (if there are any) can only pass to the second. Thus, if the truth were paradoxical, then those who follow Plato would sooner choose to believe a non-paradoxical fantasy than the actual (paradoxical) truth.
Of course, Plato probably expected truth to be non-paradoxical (as most of us do), in which case he did not see himself as making a choice between true vs. non-paradoxical belief. Rather, I suspect he intended to advocate a path that would lead to beliefs that were both true and non-paradoxical simultaneously. Nevertheless, it is telling that Plato’s method employs paradox testing prior to any other, including empirical testing. Perhaps this was because Plato trusted his sense of logic more than he trusted any of his other senses.
Modern scientists have also been known to set paradox testing above empirical testing. For example, when observing a magic show, a scientist may observe what appears to be a direct violation of physical laws. If he/she took empirical evidence as the highest authority in guiding his/her choice of what to believe in such situations, then he/she would believe that physical laws had changed, that the previous experiments confirming the old laws had now become obsolete. But we do not expect many scientists to react this way. Even when the subject matter is not a magic show, even when it is an experiment in their own controlled laboratories, we expect scientists to treat unexpected observations with suspicion until working out a comprehensive non-paradoxical body of theory to explain them.
Although paradox testing may have limited applicability regarding selection of beliefs about the external world, scientists treat it as the ultimate authority so far as its scope extends. Each scientist may hold a broader variety of beliefs privately, but, in their professional circles, paradoxical claims are strictly taboo. Scientists will not entertain paradoxical propositions at scientific symposiums, nor teach them in science courses, nor publish them in scientific journals. Paradox testing is so sacred an institution of science, that certain scientists in most every scientific field have devoted themselves primarily to its application. These scientists are called “theorists”, and some of the most highly respected scientists have been counted among their ranks.